Hitherto, in treatment of water supply and sewage, ozone and chlorine have been generally used. However, industrial waste water, recycled water, and the like may contain persistent substances that cannot be decomposed by ozone or chlorine. In particular, removal of dioxins, dioxane, and the like is a big issue. In some sites, a method has been put into practical use, in which ozone (O3) and hydrogen peroxide (H2O2) or ultraviolet rays are combined to generate hydroxyl radicals (OH radicals) having higher activity than O3 and chlorine, in treatment target water, thereby persistent substances are removed. However, the apparatus cost and the operating cost for this method are very high, and thus this method has not been popularized to a large extent. Therefore, a method in which persistent substances are removed with high efficiency by causing OH radicals generated by electric discharge to act directly on treatment target water, has been considered.
As a water treatment apparatus that performs such water treatment, an apparatus has been known which includes: treatment means having a structure of layers each having a reaction vessel capable of storing treatment target water therein and pin-shaped electrodes that generate electric discharge for performing electric discharge radical treatment on the treatment target water; and power supply means for applying a high voltage to the electrodes (see, for example, Patent Document 1). According to such a radical treatment system, it is possible to improve the decomposition efficiency of persistent substances dissolved in water, by using radicals.